1. Field of the Invention
This invention relates to a toner for developing electrostatic images or a toner for forming toner images in a toner-jet type image forming method, and a process for producing the toner. More particularly, this invention relates to a toner used preferably in a system where toner images formed by toner are heat-and-pressure fixed to printing sheets such as transfer mediums, and a process for producing such a toner.
2. Related Background Art
In electrostatic development, the system is so set up that toner particles charged electrostatically develop an electrostatic latent image formed on a photosensitive drum, by the aid of an electrostatic force acting in accordance with potential differences on the drum. Here, the toner particles are charged electrostatically by the friction between toner particles themselves or between toner particles and carrier particles. In order to cause this friction in a good efficiency and uniformly, it is important to make the toner retain a fluidity.
For such purpose, as methods commonly used to impart a fluidity to toners, a method is well known in which fluidity-providing agents such as inorganic fine particles as typified by silica, titania or alumina particles or organic fine particles comprised of polymeric compounds are externally added to toner particles surfaces. Also, the method of adding such fluidity-providing agent has many alternatives. For example, it is common to use a method in which the fluidity-providing agent is made to adhere to the surfaces of toner particles by the aid of electrostatic force, or van der Waals force, acting between toner particles and the fluidity-providing agent. This method of making the fluidity-providing agent adhere to the surfaces of toner particles is carried out using a stirrer or mixer.
In the above method, however, it is not easy to make the fluidity-providing agent adhere to the surfaces of toner particles in a uniformly dispersed state. Also, fluidity-providing agent particles not adhering to the toner particles may mutually form agglomerates, which are included in the toner in what is called a free state. It is difficult to avoid the presence of such free additives. In such a case, the fluidity of toner may decrease to cause, e.g., a decrease in quantity of triboelectricity, so that it may become impossible to attain a sufficient image density or inversely images with much fog may become formed. In addition, in conventional cases the fluidity-providing agent adheres to the surfaces of toner particles only by the aid of electrostatic force or van der Waals force as stated above. Hence, when continuous copying is made, the fluidity-providing agent may come off the surfaces of toner particles or become buried in toner particles increasingly, bringing about a problem that image quality attained at the initial stage of running can not be maintained at the latter half of continuous copying.
As a method of imparting the fluidity to toner without use of any fluidity-providing agent, a method is known in which, as disclosed in Japanese Patent Application Laid-open No. 7-181722, fine wax particles are made to stick to the surfaces of toner particles and are provided on their outer sides with polysiloxane layers obtained by polycondensation of an aminosilane alkoxide and an alkylalkoxysilane, and a method, as disclosed in Japanese Patent Application Laid-open No. 8-95284, a toner is obtained by polymerizing a monomer system to which an organosilane compound has been added. The toners obtainable by these methods, however, have smooth toner particle surfaces, and hence have had the problem of causing a lowering of transfer efficiency.
In addition, in the field of electrophotography, it has recently been more strongly required to form images with a higher image quality. Then, as a means for achieving a high image quality of images, toners used in developers may be made to have a sharp charge quantity distribution. When toners have a sharp charge quantity distribution, individual toner particles constituting the toner can be charged in a uniform quantity. Hence, images formed may have less fog or black spots around images and it becomes possible to reproduce toner images faithful to latent images formed on the photosensitive drum. In general, the charge quantity of toner particles is proportional to the particle diameter of toner particles. Accordingly, in order to make the toner have a sharp charge quantity distribution, it is thought to be effective to make the toner have a sharp particle size distribution. In order to impart electric charge to toner particles in a sufficient quantity, commonly employed is a method of adding what is called external additives such as inorganic fine particles as typified by silica, titania or alumina particles or organic fine particles comprised of polymeric compounds.
Since, however, it is common for such external additives to be made to stick mechanically to the surfaces of toner particles by means of a stirrer or mixer, the external additive may become released from toner particles or inversely become buried in toner particles. Such a phenomenon may occur especially when continuous printing is made. Then, this phenomenon may cause a change in the surface state of toner particles. Hence, when images are formed, it may become difficult to continuously maintain the charge quantity of toner kept at the running initial stage, and become difficult to maintain the initial sharp charge quantity distribution during the running. The external additives have had such problems.
Moreover, in recent years, with a surprising spread of personal computers, the demand for printers and copying machines employing electrophotographic systems shows a tendency of expanding from those for offices toward those for general users. With such a tendency, these printers and copying machines of electrophotographic systems are sought to be made small-sized as apparatus, to achieve energy saving for ecological requirement and to be made low-cost. As a method of settling these subjects, fixing temperature may be made lower. As a means for its achievement, it is attempted that binder resins constituting toners are made to have a lower molecular weight or a lower glass transition point (Tg), or waxes are incorporated into toner particles in a larger content.
Making binder resins have a lower molecular weight or have a lower glass transition point (Tg) can make melting temperature lower. However, such toners may concurrently have a poor storage stability to cause in-machine melt adhesion, or mutual melt adhesion of toner particles to have a low fluidity, especially in an environment of high temperature.
To solve such problems, methods are proposed in which silane compounds are used. For example, Japanese Patent Application Laid-open No. 7-98516 discloses a method in which a polyester resin and a metal alkoxide are kneaded and cross-linked. Also, Japanese Patent Application Laid-open No. 7-239573 discloses a method in which a vinyl type resin formed by covalent linkage of a vinyl monomer and a silane coupling agent having an unsaturated double bond and an alkoxysilyl group is used as a binder resin. In these methods, however, the binder resin is compositionally limited, or silane compounds are present even inside the toner particles. Thus, it has substantially been difficult to control fixing performance and storage stability which are performances conflicting with each other.
There are other methods. For example, Japanese Patent Application Laid-open No. 6-289647 discloses a method in which toner particles are coated with a curable silicone resin; Japanese Patent Application Laid-open No. 8-15894, a method in which a metal alkoxide is made to adhere to the surfaces of toner particles; and Japanese Patent Application Laid-open No. 9-179341, a method in which toner particles are provided with covering in the form of continuous thin films using a silane coupling agent. These methods are attempts to prepare base particles by the use of a resin having a relatively low Tg and coating their surfaces with a hard material such as a silicone resin or a metal alkoxide so that toner particles can be prevented from blocking and at the same time fixing temperature can be made lower. The surfaces of toner particles, however, are not well covered with the silane compound or, even when covered, the surfaces of coating layers are smooth, and hence the toner particles have small contact areas on fixing members such as a heat roll and may have a poor heat absorption efficiency, resulting in a great difference between the Tg and an actual melting temperature of the base particles. Thus, it has been difficult to achieve satisfactory low-temperature fixing.
An object of the present invention is to provide a toner having a superior fluidity even without use of any fluidity-providing agent and yet can attain a high transfer efficiency, and a process for producing such a toner.
Another object of the present invention is to provide a toner making use of no fluidity-providing agent so as to provide a toner which no longer has any possibility that the fluidity-providing agent becomes released from or buried in toner particles, even when development is repeated continuously, can maintain a stable image density even after long-time running, and has a superior fixing performance, and a process for producing such a toner.
A still another object of the present invention is to provide a toner that can maintain its sharp charge quantity distribution throughout running of long-time image reproduction, whereby high-quality images having less fog and black spots around images and having a high dot reproducibility can stably be obtained, and a process for producing such a toner.
A further object of the present invention is to provide a toner having superior anti-blocking properties in spite of its good low-temperature fixing performance, and a process for producing such a toner.
To achieve the above objects, the present invention provides a toner comprising toner particles composed of at least a binder resin and a colorant, wherein the toner particles each have a coating layer formed on their surfaces in a state of particulate matters being stuck to one another; the particulate matters containing at least a silicon compound.
The present invention also provides a process for producing a toner, comprising the steps of;
producing toner particles composed of at least a binder resin and a colorant; and
building up a polycondensate of a silicon compound on the surfaces of the toner particles from the outside of the particles to form on each toner particle surface a coating layer in a state of particulate matters being stuck to one another; the particulate matters containing at least a silicon compound.
The present invention still also provides a process for producing a toner, comprising the steps of;
producing toner particles composed of at least a binder resin and a colorant and having a silicon compound present internally; and
allowing the toner particles to react in an aqueous medium selected from the group consisting of water and a mixed solvent of water and a water-miscible solvent, to cause the silicon compound to undergo hydrolysis and polycondensation on the surfaces of the toner particles to form on each toner particle surface a coating layer in a state of particulate matters being stuck to one another; the particulate matters containing at least the silicon compound.
The toner of the present invention is characterized in that the surfaces of toner particles composed of at least a binder resin and a colorant, constituting the toner, are each provided with a coating layer formed in a state of particulate matters being stuck to one another, containing at least a silicon compound. In the present invention, the coating layer formed in a state of particulate matters being stuck to one another, containing at least a silicon compound, refers specifically to a layer formed on each toner particle surface by hydrolysis and polycondensation of a silicon compound typified by a silane alkoxide, and preferably a layer so formed that fine unevenness on the order of nanometer (nm) is observable on the surface.
As a result of extensive studies, the present inventors have discovered that a toner provided with a sufficient fluidity can be obtained without use of any conventional external additive when the above coating layer formed in a state of particulate matters being stuck to one another, containing at least a silicon compound, is provided on each surface of the toner particles composed of at least a binder resin and a colorant. Thus, they have accomplished the present invention. It has been found that this enables the toner to retain a stable charging performance. It has also been found that, since no external additive is used, the toner no longer has any possibility that the fluidity-providing agent becomes released from or buried in toner particles, even when development is repeated continuously, and promises a superior running performance.
xe2x80x9cThe coating layer formed in a state of particulate matters being stuck to one another, containing at least a silicon compoundxe2x80x9d provided on the toner particle surface will be described in detail.
As a result of studies made on the state of particle surface of the toner having good performances as stated above, the present inventors have reached the following findings. First, cross sections of particles constituting the toner of the present invention were observed with a transmission electron microscope (TEM). This enabled observation of how a layer structure is formed which is constituted of particulate matters with a diameter of tens of nanometers (nm) each.
The surface configuration of toner particles before and after the washing of toner with a surface-active agent was further examined by electron probe microanalysis (EPMA) using a scanning electron microscope (SEM) fitted with an X-ray microanalyzer. As a result, obtained was the result that the percent loss of silicon atoms that results from the washing was small. It was also ascertainable that the particulate matters containing a silicon compound do not merely adhere to the toner particle surface but are present in such a state that the particulate matters are stuck to one another to from a coating layer.
The layer structure of the coating layer which is a requirement constituting the present invention, formed on the toner particle surface in a state of particulate matters being stuck to one another, containing at least a silicon compound, (hereinafter often xe2x80x9ccoating layer formed of silicon-compound-containing particulate matters being stuck to one anotherxe2x80x9d) is ascertained in the manner described below in detail.
In the present invention, the fact that the coating layers formed on toner particle surfaces are in a state of particulate matters being stuck to one another, containing at least a silicon compound, is ascertained in the following way.
Coating Layer Formed of Silicon-compound-containing Particulate Matters Being Stuck to One Another
To ascertain the presence of the layer structure by observation with a transmission electron microscope:
Particles of toner to be examined are buried in epoxy resin, and thereafter ultra-thin slices of the particles of toner are prepared using a microtome. The slices are fastened to a measuring cell for the transmission electron microscope. This is used as a sample.
The sample is observed with a transmission electron microscope H-7500 (manufactured by Hitachi Ltd.) at 10,000 to 50,000 magnifications to ascertain that the layer structure formed of the particulate matters is present on the toner particle surface.
To ascertain the particulate matters being stuck to one another, on the basis of the percent loss of silicon atoms present on the particle surfaces of toner after washing with a surface-active agent:
(1) Measurement by electron probe microanalysis (EPMA) to determine the quantity (% by weight) of silicon atoms present on particle surfaces of toner:
The particle surfaces of the toner are examined by means of a field-emission scanning electron microscope S-4500 (manufactured by Hitachi Ltd.) fitted with an X-ray microanalyzer X-5770W (manufactured by Horiba Seisakusho K.K.) to make electron probe microanalysis (EPMA) under conditions of an accelerating voltage of 20 kV, a sample absorption electric current of 1.0xc3x9710xe2x88x9210 A and 25,000 magnifications. Quantity (concentration) Si1 (% by weight) of silicon atoms present thereon where the total sum of quantities (% by weight) of carbon atoms, oxygen atoms and silicon atoms is regarded as 100% is measured. The measurement is made in 20 visual fields, and an average value thereof is regarded as a measured value.
(2) Washing particle surfaces of toner with surface-active agent:
0.2 g of toner is dispersed in 5 ml of an aqueous 5% by weight dodecylbenzenesulfonic acid solution. The dispersion obtained is set on an ultrasonic cleaner for 30 minutes to wash the particle surfaces of the toner thoroughly. Centrifugal separation and washing are further repeated to remove the dodecylbenzenesulfonic acid completely from the particle surfaces of the toner, followed by drying under reduced pressure to separate the toner.
(3) Measurement of the quantity (% by weight) of silicon atoms present on particle surfaces of toner after washing with surface-active agent:
To measure the quantity (% by weight) of silicon atoms which had been present on the particle surfaces of the toner and has been removed therefrom as a result of the above operation (2), the particle surfaces of the toner having been washed with the surface-active agent are examined by electron probe microanalysis (EPMA) in the same manner as in the above (1), to measure a quantity Si2 (% by weight) of silicon atoms present.
(4) Analysis of the state of the coating layer provided on the toner particle surface and formed of particulate matters containing a silicon compound:
From the values of Si1 and Si2 obtained by the above procedure of (1) to (3), the percent loss of the quantity of silicon atoms present on the toner particles, resulting from the washing with surface-active agent, is calculated according to the following expression. In an instance where the percent loss of the quantity of silicon atoms present on the particle surfaces of the toner is extremely small, the coating layer formed on the toner particle surface, formed of the particulate matters containing a silicon compound, can be judged to stand adherent in such a state that it may come off the particle surface with difficulty. Accordingly, in an instance where the percent loss of the quantity of silicon atoms present on the particle surfaces of the toner, calculated according to the following expression, is not more than 30%, the coating layer formed on the toner particle surface is regarded as a layer in which the particulate matters containing a silicon compound stand stuck firmly to one another. This is used as means for ascertaining whether or not the particulate matters containing a silicon compound stand stuck to one another.
Percent loss (%) of quantity of silicon atoms present on particles=(1xe2x88x92Si2/Si1)xc3x97100
(wherein Si1 represents a quantity of silicon atoms present on particle surfaces of toner before the washing with surface-active agent, and Si2 represents a quantity of silicon atoms present on particle surfaces of toner after the washing with surface-active agent.)
As described above, in the present invention, the result obtained by visually ascertaining with a transmission electron microscope the layer structure formed of particulate matters is combined with the result obtained by measuring the percent loss of silicon atoms on the particle surfaces of the toner after the washing with surface-active agent. This combination is used as means for ascertaining xe2x80x9cthe coating layer formed in a state of particulate matters being stuck to one another, containing at least a silicon compoundxe2x80x9d.
As ascertained by the above method, in the toner of the present invention, the coating layers present on the toner particles constituting the toner are each formed of particulate matters being stuck to one another, containing at least a silicon compound. Thus, it follows that fine unevenness is present on the toner particle surfaces. This enables achievement of a high transfer efficiency. Also, in the present invention, the coating layers are formed on the toner particle surfaces by a silicon compound polycondensate produced by a sol-gel process described later as a typical example of a toner production process. According to this process, the polycondensate takes the form of a film, and also the film has the form of a coating layer which covers the whole of each toner particle surface as a film formed in a state where particulate matters containing a polycondensate of a silicon compound are chemically combined with one another. Hence, there is no room for any free fine particles not adhering to toner particles or any free fine particles due to deterioration by running which are ascribable to the addition of fluidity-providing agent as in the case when the conventional fluidity-providing agent such as silica is made to adhere to toner particle surfaces as stated previously. Thus, the toner of the present invention can have a superior running performance.
Detailed studies made by the present inventors have revealed that, when the quantity of silicon atoms present on the particle surfaces of the toner is measured by electron probe microanalysis (EPMA), the quantity of their presence may preferably be in the range of from 0.10 to 20.0% by weight, more preferably in the range of from 0.1 to 10.0% by weight, and still more preferably in the range of from 0.10 to 4.0% by weight, to obtain a coating layer in a more preferred state. More specifically, it has been confirmed that a higher fluidity and a high transfer efficiency can be imparted to the toner when the surfaces of toner particles are provided with coating layers formed of particulate matters being stuck to one another, containing such a silicon compound that may provide the quantity of silicon atoms present on the particle surfaces of toner which is at least 0.10% by weight. Also, when the quantity of silicon atoms present on the toner particle surfaces provided with such coating layers is at least 0.10% by weight, the toner particle surfaces can be covered sufficiently with such coating layers. Hence, a higher fluidity can be imparted to the toner, and a toner that can be charged in a sufficient quantity can be obtained.
Meanwhile, it has been fount that the toner exhibits a better fixing performance when the coating layer is so provided that the quantity of silicon atoms present on the particle surfaces of the toner is not more than 20.0% by weight. This is presumably because the binder resin constituting the toner particles well exhibits its thermoplasticity when the toner particles are provided with the coating layers in which the quantity of silicon atoms present on the particle surfaces of the toner fulfills the above conditions.
In the present invention, the surfaces of toner particles serving as base particles are provided with the specific coating layers as described above. Hence, the binder resin constituting the toner can be made to have a lower melt temperature and can be improved in fixing performance. Even a toner having such a form does not cause, even in an environment of high temperature, any in-machine melt-adhesion or any mutual melt-adhesion of toner which may cause a lowering of fluidity. Thus, a toner simultaneously satisfying the function to promise a good storage stability can be obtained.
The toner having such a superior fixing performance may preferably be so constituted that it has at least one glass transition point at temperatures of 60xc2x0 C. or below, has a melt-starting temperature of 100xc2x0 C. or below, and also has a difference of 38xc2x0 C. or smaller between the glass transition point and the melt-starting temperature.
In the case of the toner constituted as described above, preferable coating layers can be obtained when the quantity of silicon atoms present on the particle surfaces of the toner as measured by electron probe microanalysis (EPMA) is in the range of from 0.10 to 10.0% by weight, and preferably in the range of from 0.10 to 4.0% by weight.
Since the surfaces of toner particles are provided with the coating layers formed of particulate matters being stuck to one another, containing such a silicon compound that may provide the quantity of silicon atoms present on the particle surfaces of toner which is at least 0.10% by weight, it becomes possible for sol-gel films to envelop toner particles well, showing superior anti-blocking properties, as so presumed. On the other hand, if the quantity of silicon atoms present on toner particle surfaces provided with the coating layers formed of silicon-compound-containing particulate matters being stuck to one another is less than 0.10% by weight, this means that sol-gel films are present on the particle surfaces in a small quantity, so that the sol-gel films cover the toner particles insufficiently, resulting in damage of anti-blocking properties of the toner.
Where the coating layers are so provided that the quantity of silicon atoms present on the particle surfaces of the toner is not more than 10.0% by weight, the toner particles can retain a good fixing performance. More specifically, when such coating layers are formed, the thermoplasticity of the binder resin constituting the toner particles is by no means damaged by providing the coating layers, and can be well exhibited.
In addition, since the coating layers formed on the surfaces of toner particles are formed of at least silicon-compound-containing particulate matters being stuck to one another, the surfaces of toner particles constituting the toner have fine unevenness as stated previously. This makes surface areas of toner particles larger, and hence fixing members such as a heat roll and the toner have a larger contact area, bringing about an improvement in heat absorption efficiency. As the result, compared with toners comprising toner particles having coating layers which are conventionally formed for the purpose of anti-blocking properties, a difference may less be produced between the Tg and melt-starting temperature of the toner particles and those of the toner. Hence, a sufficiently low-temperature fixing performance can be achieved.
In addition, as stated previously, the coating layers provided on the toner particle surfaces are formed by building up a polycondensate of a silicon compound by a sol-gel process described later as a typical example. The polycondensate takes the form of a film, and the film having the form of a coating layer in which the film formed in a state where particulate matters containing a polycondensate of a silicon compound are chemically combined with one another covers the whole of each toner particle surface. Hence, the surfaces of toner particles in which the binder resin having a low glass transition point and promising a good low-temperature fixing performance is used as the chief component can be enveloped. As the result, the toner can be free from any mutual melt-adhesion even in an environment of high temperature.
Studies made by the present inventors have further revealed that, in order to make the above coating layers have the advantageous function as stated previously, it is necessary for the coating layer to stand chiefly formed on the toner particle surface and in the vicinity thereof. More specifically, it has been found that if, e.g., the above polycondensate of a silicon compound, which is a preferred constituent of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, is present up to the interiors of particles of the toner, the binder resin constituting the toner particles may lose its thermoplasticity to tend to damage the fixing performance of the resulting toner.
In this regard, as a result of detailed studies further made by the present inventors, the following has been ascertained: As a requirement for the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, formed on the toner particle surface and in the vicinity thereof, the quantity (% by weight) of silicon atoms present in cross sections of particles of the toner where the total sum of quantities of carbon atoms, oxygen atoms and silicon atoms present therein is regarded as 100% may be not more than 4.0% by weight as a value measured by electron probe microanalysis (EPMA), within the value of which a toner having a sufficient fixing performance can be obtained. More specifically, if the quantity of silicon atoms present in the particle cross sections of the toner is more than 4.0% by weight, it means that the polycondensate of a silicon compound, which is a constituent of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another is present up to the interiors of particles of the toner. As the result, the fixing performance is damaged, as so presumed.
The quantity (% by weight) of silicon atoms present in the particle cross sections of the toner as defined in the present invention is measured in the manner as described below.
Measurement of the quantity of silicon atoms present in particle cross sections of toner:
Particles of toner for measurement are buried in epoxy resin, and thereafter ultra-thin slices of the particles of toner are prepared using a microtome. These are used as a sample. This sample is put on a sample rack made of aluminum, used for scanning electron microscopy, and is fastened with a conductive carbon pressure-sensitive adhesive sheet. On this sample, silicon atoms are determined in the same manner as the above measurement of the quantity of silicon atoms present on the particle surfaces of the toner.
In the toner of the present invention, a more preferable effect can be obtained when the quantity of silicon atoms present on the particle surfaces of the toner is twice or more the quantity of silicon atoms present in the particle cross sections of the toner. More specifically, studies made by the present inventors have revealed that a better fixing performance can be attained when images are formed using a toner comprising toner particles each provided with the coating layer formed of silicon-compound-containing particulate matters being stuck to one another that meets such a requirement. This is presumably because, since the coating layer having such a configuration is formed on the toner particle surface and in a more vicinity thereof, the thermoplasticity of binder resin is not damaged by the formation of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, bringing about an improvement in fixing performance.
It has also been found that a more preferable effect can be obtained when the quantity of silicon atoms present on the particle surfaces of the toner is not more than 4.0% by weight. Then, it has also been found that such constitution can be achieved with ease by using a silicon compound having an organic substituent, as the silicon compound contained in the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, and this can bring about a more improvement in the running performance of the toner. This is considered to be presumably because the use of the silicon compound having an organic substituent, as the silicon compound contained in the above coating layer additionally provides the resulting coating layer with a flexibility attributable to organic chains, so that a superior running performance has been achieved.
More specifically, in the case when the silicon compound contained in the coating layer formed of silicon-compound-containing particulate matters being stuck to one another has an organic substituent, it is thought that the quantity of carbon atoms present on the particle surfaces of the toner is made larger, in other words, the quantity of silicon atoms present on the particle surfaces of the toner where the total sum of quantities of carbon atoms, oxygen atoms and silicon atoms is regarded as 100% is made smaller. However, as a result of studies made by the present inventors on the relationship between the quantity of silicon atoms present on the particle surfaces of the toner and the running performance of the running performance of the toner, it has been found that the coating layers to be formed can be more improved in durability when the quantity of silicon atoms present on the particle surfaces of the toner where the total sum of quantities of carbon atoms, oxygen atoms and silicon atoms is regarded as 100% is not more than 4.0% by weight, and this can bring about a more improvement in running performance of the toner of the present invention.
In the toner of the present invention, comprising toner particles provided with the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, unreacted silanol groups (xe2x80x94SiOH) remain on the toner particle surfaces in some cases. Accordingly, in order for the toner to retain a sufficient charge quantity in an environment of high temperature and high humidity, the surface of the coating layer may preferably be treated with a coupling agent.
More specifically, where the surface of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another is treated with a coupling agent, the hydroxyl groups of the unreacted silanol groups having remained on the toner particle surfaces are capped with the coating layers provided on the toner particle surfaces. Hence, the toner can be less affected by the atmospheric moisture and can retain a sufficient charge quantity even in an environment of high temperature and high humidity. Thus, the function of the coating layers present on the toner particle surfaces, stated previously, can be more enhanced.
In the present invention, the toner may have a small diameter and a sharp particle size distribution, having a number-average particle diameter of from 0.1 xcexcm to 10.0 xcexcm and a coefficient of variation in number distribution, of 20.0% or less. This is preferable in order to form high-quality images.
Controlling the size and particle size distribution of the toner in this way makes the toner have a sharp charge quantity distribution when such a toner is used, thus it becomes possible to obtain images with less black spots around images and a high dot reproducibility. If the toner has a number-average particle diameter smaller than 0.1 xcexcm, the toner may be handled with difficulty as a powder. If it has a number-average particle diameter larger than 10.0 xcexcm, the toner may have so excessively large a particle diameter with respect to latent images that it may be difficult to reproduce dots faithfully. Also, a toner having a coefficient of variation in number distribution, of more than 20.0% may have uneven charge quantity to form images with much fog and many black spots around images, resulting in a low dot reproducibility.
In the present invention, in order to achieve the objects as stated previously, the toner may more preferably have a number-average particle diameter of from 1.0 xcexcm to 8.0 xcexcm, and still more preferably from 3.0 xcexcm to 5.0 xcexcm, and the toner may more preferably have a coefficient of variation in number distribution, of 15.0% or less, and still more preferably 10.0% or less.
The toner in which the coating layers as described above are provided on the surfaces of toner particles having a sharp particle size distribution can retain its charge quantity distribution even after long-time running.
The number-average particle diameter and particle size distribution of the toner as used in the present invention are measured in the manner described below.
First, a photograph of the toner is taken with a field-emission scanning electron microscope S-4500 at 5,000 magnifications, manufactured by Hitachi Ltd. From this photograph, particle diameter of each toner particle is measured on toner particles so as to be measured on 300 partciles or more in cumulation. From the measurements obtained, the number-average particle diameter is calculated. Also, the coefficient of variation in number distribution of the toner is determined from the following expression.
Coefficient of variation (%)=(standard deviation of number distribution)/(number-average particle diameter)xc3x97100
In addition to the shape-related features described above, the toner of the present invention may preferably have, in its thermal properties, at least one glass transition point at temperatures of 60xc2x0 C. or below, have a melt-starting temperature of 100xc2x0 C. or below and also have a difference of 38xc2x0 C. or smaller between the glass transition point and the melt-starting temperature. This can materialize a fixing temperature lower than conventional fixing temperatures, and also can satisfy, as stated previously, anti-blocking properties on account of the coating layers provided on the toner particle surfaces.
The above specific thermal properties of the toner will be detailed below.
Studies made by the present inventors have revealed that the toner does not exhibit any good fixing performance in some cases in the fixing performance test described layer, if the toner does not satisfy the requirements that it has at least one glass transition point at temperatures of 60xc2x0 C. or below and also has a melt-starting temperature of 100xc2x0 C. Also, if it has a difference greater than 38xc2x0 C. between the glass transition point and the melt-starting temperature, the low-temperature fixing performance possessed by the toner particles can not be retained and the toner whose toner particles have been coated with sol-gel films can not exhibit a good fixing performance in the fixing performance test.
In order to control the melt-starting temperature and glass transition point of the toner in the manner described above, the thermal properties of toner particles serving as base particles (toner particles having not provided with the coating layers) may be controlled by controlling, e.g.;
1) composition of the binder resin;
2) molecular weight and molecular weight distribution of the binder resin; and
3) content of a wax or release agent.
Then, the thermal properties may preferably be so controlled that the toner particles have at least one glass transition point (Tg) at temperatures of 60xc2x0 C. or below, and more preferably 40xc2x0 C. or below, and have a melt-starting temperature of 100xc2x0 C. or below, and more preferably 80xc2x0 C. or below.
In the case when the melt temperature is controlled by controlling the content of a release agent incorporated in the toner, the use of a release agent in a content more than 80% by weight based on the weight of the toner inclusive of the coating layers may cause come-off of images once fixed on transfer paper or film, and is supposed to be substantially impractical. Taking account of releasability from fixing rollers, the form incorporated with the release agent can be said to be preferred. Accordingly, in the toner of the present invention, the release agent may preferably be in a content ranging from 5 to 80 parts by weight, and more preferably from 10 to 60 parts by weight, based on the total weight of the toner.
As release agents usable in the present invention, solid waxes are preferred. Stated specifically, solid waxes which are solid at room temperature are preferred. They may specifically include, e.g., paraffin wax, polyolefin wax, Fischer-Tropsch wax, amide waxes, higher fatty acids, ester waxes, and derivatives thereof such as graft compounds or block compounds thereof. Ester waxes having at least one long-chain ester moiety having at least 10 carbon atoms as shown by the following structural formulas are particularly preferred as being effective for high-temperature anti-offset properties without impairment of the transparency required for OHP.
Structural formulas of the typical compounds of preferable specific ester waxes usable in the present invention are shown below as general structural formulas (1) to (5).
[R1xe2x80x94COOxe2x80x94(CH2)nxe2x80x94]axe2x80x94[xe2x80x94(CH2)mxe2x80x94OCOxe2x80x94R2]bxe2x80x83xe2x80x83(1)
wherein a and b each represent an integer of 0 to 4, provided that a+b is 4; R1 and R2 each represent an organic group having 1 to 40 carbon atoms, provided that a difference in the number of carbon atoms between R1 and R2 is 10 or more; and n and m each represent an integer of 0 to 15, provided that n and m are not 0 at the same time.
[R1xe2x80x94COOxe2x80x94(CH2)nxe2x80x94]axe2x80x94Cxe2x80x94[xe2x80x94(CH2)mxe2x80x94OH]bxe2x80x83xe2x80x83(2)
wherein a and b each represent an integer of 0 to 4, provided that a+b is 4; R1 represents an organic group having 1 to 40 carbon atoms; and n and m each represent an integer of 0 to 15, provided that n and m are not 0 at the same time.
[R1xe2x80x94COOxe2x80x94(CH2)nxe2x80x94]axe2x80x94Cxe2x80x94[xe2x80x94(CH2)mxe2x80x94OH]bxe2x80x83xe2x80x83(3)
wherein a and b each represent an integer of 0 to 3, provided that a+b is 3 or less; R1 represents an organic group having 1 to 40 carbon atoms; and n and m each represent an integer of 0 to 15, provided that n and m are not 0 at the same time.
R1xe2x80x94COOR2xe2x80x83xe2x80x83(4)
wherein R1 and R2 each represent a hydrocarbon group having 1 to 40 carbon atoms; and R1 and R2 may have the number of carbon atoms which is the same or different from each other.
R1COO(CH2)nOOCR2xe2x80x83xe2x80x83(5)
wherein R1 and R2 each represent a hydrocarbon group having 1 to 40 carbon atoms; n represents an integer of 2 to 20; and R1 and R2 may have the number of carbon atoms which is the same or different from each other.
The glass transition point and melt-starting temperature used in the present invention are measured in the manner as described below.
Measurement of glass transition point:
The glass transition point Tg of resin is measured according to a method prescribed in ASTM D3418, using a differential thermal analyzer DSC-7, manufactured by Perkin Elmer Co.
Measurement of melt-starting temperature:
The melt-starting temperature in the present invention is measured with a flow tester CFT-500 (manufactured by Shimadzu Corporation). A sample for measurement is weighed in an amount of about 1.0 to 1.5 g. This is pressed for 1 minute using a molder under application of a pressure of 9,806.65 kPa (100 kgf/cm2) to prepare a pressed sample.
This pressed sample is put to the measurement with the flow tester in an environment of normal temperature and normal humidity (temperature: about 20-30xc2x0 C.; humidity: 30-70%RH) under the following conditions to obtain a humidity-apparent viscosity curve. From the smooth curve obtained, the temperature at which the viscosity begins to decrease is read, and is regarded as the melt-starting temperature.
Rate temperature: 6.0xc2x0 C./minute
Set temperature: 70.0xc2x0 C.
Maximum temperature: 200.0xc2x0 C.
Interval: 3.0xc2x0 C.
Preheating: 300.0 seconds
Load: 20.0 kg
Die (diameter): 1.0 mm
Die (length): 1.0 mm
Plunger: 1.0 cm2 
The toner production process will be described below by which the toner of the present invention which is so made up that its toner particles have on their surfaces the coating layers formed of silicon-compound-containing particulate matters being stuck to one another.
In the toner production process of the present invention, toner particles composed of at least a binder resin and a colorant are prepared and then, on their surfaces, the coating layers formed of silicon-compound-containing particulate matters being stuck to one another are formed in the manner as described later. As the toner particles, any of those conventionally known may be used as long as they are toner particles composed of at least a binder resin and a colorant and optionally containing various additives. More specifically, the toner particles used in the present invention may be those of what is called the pulverization toner, obtained by kneading a toner material composition comprised of a binder resin and other optional components, cooling the kneaded product obtained, followed by pulverization, or what is called the polymerization toner, obtained by polymerizing polymerizable monomers that form a binder resin. In the toner of the present invention, however, spherical toner particles may preferably be used as the toner particles because, if toner particles have no specific shape, the above coating layers formed on their surfaces tend to deteriorate. Such spherical toner particles may be obtained with ease by sphering toner particles produced by pulverization or producing toner particles by polymerization.
As a typical example for producing the toner particles according to the present invention, having on their surfaces the coating layers formed of silicon-compound-containing particulate matters being stuck to one another, a method commonly called a sol-gel process may be applied. An example for producing the toner particles by this sol-gel process is described below.
The sol-gel process is commonly known as a method for producing planar metal compound polycondensation films or solid-state metal compound polycondensates. Metal compound films formed by this method are commonly called sol-gel films.
The sol-gel films are, stated specifically, films formed by hydrolysis-polycondensation of silicon compounds typified by silane alkoxides, and having surfaces on which fine unevenness on the order of nanometer (nm) is observable. As a result of extensive studies, the present inventors have discovered that, without use of any external additive used in conventional toners, a toner which can retain a sufficient charge quantity and may hardly cause a lowering of performance of toner as a result of running can be obtained by providing the sol-gel films on the toner particle surfaces.
As a result of extensive studies, the present inventors have also found that, when the sol-gel films having the properties described above are provided on the toner particle surfaces, the toner containing a binder resin having a low Tg can be free from blocking while keeping its low-temperature fixing performance.
As a first embodiment of the process by which the coating layer formed of silicon-compound-containing particulate matters being stuck to one another is formed on the toner particle surface, a process may be used which comprises producing toner particles composed of at least a binder resin and a colorant, and building up a polycondensate of a silicon compound on the surfaces of the toner particles from the outside of the particles to form on each toner particle surface the above coating layer.
Stated specifically, this is a process in which the toner particles serving as base particles (hereinafter often xe2x80x9cbase-particle toner particlesxe2x80x9d) are dispersed in an aqueous medium comprising water or a mixed solvent of a water-miscible solvent and water in which medium a silane alkoxide has been dissolved and thereafter the aqueous dispersion obtained is added dropwise to water or other aqueous medium in which an alkali has been added. According to this process, the silane alkoxide having been dissolved in the aqueous dispersion containing toner particles causes hydrolysis and polycondensation in the presence of the alkali to become gradually insoluble, and is further built up on the toner particle surface by hydrophobic mutual action. As the result, the coating layer formed of silicon-compound-containing particulate matters being stuck to one another is formed on the toner particle surface. In the case when the toner particles produced by polymerization are used, the reaction system after the polymerization is completed to form the toner particles serving as base particles may be cooled to room temperature and thereafter the silane alkoxide may be dissolved therein so as to be used as an aqueous toner dispersion.
As the water-miscible solvent that may be used in the above process, organic solvents including alcohols as exemplified by methanol, ethanol and isopropanol may be used. With an increase in organicity (i.e., the number of carbon atoms) of these solvents, the solubility of the silane alkoxide polycondensate increases to make it difficult for the silane alkoxide polycondensate to be built up on the toner particle surface. Accordingly, methanol or ethanol may preferably be used as the water-miscible solvent.
As a second embodiment of the process by which the coating layer formed of silicon-compound-containing particulate matters being stuck to one another is formed on the toner particle surface, a process may be used which comprises producing toner particles composed of at least a binder resin and a colorant and having a silicon compound present internally, and dispersing the toner particles in an aqueous medium selected from the group consisting of water and a mixed solvent of water and a water-miscible solvent to cause the silicon compound to undergo hydrolysis and polycondensation reaction on the surfaces of the toner particles, to form on each toner particle surface the above coating layer.
In the above process, the toner particles are dispersed in water or a mixed solvent of water and a water-miscible solvent, whereupon the silicon compound made present in the toner particles comes into contact with water to undergo hydrolysis. Namely, sol-gel reaction takes place only on the toner particle surfaces and in the vicinity thereof. After the reaction is completed, the toner particles may be washed with a solvent such as an alcohol to remove any unreacted silicon compound remaining inside the toner particles. As the result, a polycondensate of the silicon compound becomes present selectively on the toner particle surfaces. Thus, the coating layers formed of silicon-compound-containing particulate matters being stuck to one another and in which the quantity of silicon atoms present on the toner particle surfaces is larger than the quantity of silicon atoms present inside the toner particles can be formed on the toner particle surfaces.
The aqueous medium used when the toner particles are dispersed, which is preferred in the above process, may include water and a mixed solvent of water and a water-miscible solvent including alcohols such as methanol, ethanol and propanol.
As methods by which the silicon compound is made previously present inside the toner particles, the silicon compound may be made present mixedly when the toner particles are produced, or may be introduced into particles obtained after the toner particles serving as base particles are produced by a conventional method. In the latter method, it is effective to use a method in which the silicon compound is made to permeate into the toner particles in water or a mixed solvent of water and a water-miscible solvent. Stated specifically, such a method may include the following method.
For example, a method is available in which the toner particles serving as base particles and the silicon compound are dispersed in a liquid medium in which the silicon compound is slightly soluble, as typified by water. In such a method, the silicon compound having slightly dissolved in the liquid medium is dispersed into the liquid medium to become absorbed in the toner particles, or the silicon compound having been dispersed physically comes into contact with the toner particles to become absorbed in the toner particles, thus the silicon compound can be introduced into the toner particles.
In such a method, in order to disperse the silicon compound stably in the liquid medium, it is preferable to use a surface-active agent. As the surface-active agent, any conventionally known surface-active agents commonly used may be used.
Here, a dispersion of the toner particles and a dispersion of the silicon compound may separately be prepared and the both may be mixed. In such an instance, if the dispersion of the silicon compound is added to the dispersion of the toner particles, the toner particles tend to coalesce to undesirably provide a toner having a broad particle size distribution than the toner particles before reaction. As the result, the toner to be obtained may have a broad triboelectric charge distribution to tend to cause difficulties such as black spots around images. Accordingly, in the instance where a dispersion of the toner particles and a dispersion of the silicon compound are separately prepared and the both are mixed, it is preferable to add the dispersion of the toner particles to the dispersion of the silicon compound.
The particle size distribution the toner particles have had before the coating layers are formed should be retained after the coating layers have been formed on the toner particle surfaces to produce the toner of the present invention. To this end, when the silicon compound is dispersed in the liquid medium such as water, the silicon compound may preferably be dispersed in the form of droplets as small as possible with respect to individual toner particles. Also, as methods therefor, it is preferable to use a method in which materials are stirred mechanically by means of a high-speed stirrer and a method in which the silicon compound is finely dispersed by means of an ultrasonic dispersion machine.
In the case when the silicon compound is made to permeate into toner particles so as to be made present therein, the silicon compound may be made to permeate into toner particles using the silicon compound and other slightly water-soluble solvent in combination for the purpose of improving the rate of permeation as a supplementary means.
As the slightly water-soluble solvent used here, any solvents may be used as long as they are solvents more hydrophilic than the silicon compound used and are solvents slightly soluble in water. Stated specifically, they may include, e.g., isopentyl acetate, isobutyl acetate, methyl acetate and ethyl acetate. In use of any of these slightly water-soluble solvents, the slightly water-soluble solvent must be removed from the interiors of toner particles by evaporating it, or by introducing toner particles into a hydrophobic medium and dissolving the slightly water-soluble solvent in the hydrophobic medium. The operation thus made also enables removal of the unreacted silicon compound remaining in toner particles.
As another method by which the silicon compound is made to permeate into base-particle toner particles so as to be made present therein, the toner particles may be dispersed in a liquid medium (aqueous medium) in which the silicon compound is soluble, as exemplified by an alcohol, to make the silicon compound have a low solubility to incorporate the silicon compound into toner particles. As methods for making the silicon compound have a low solubility, for example, temperature may be lowered, or a liquid medium i) which is soluble in the liquid medium in which the silicon compound is soluble and also ii) in which the silicon compound is insoluble is added slowly. The latter method may specifically include a method in which, e.g., the silicon compound is dissolved in a low-molecular weight alcohol such as methanol, the base-particle toner particles are dispersed therein, and thereafter water is added slowly to make the silicon compound have a low solubility, thus the silicon compound is permeated into the toner particles to become present therein.
In the case when as described above the method of dissolving the silicon compound in a medium and incorporating it into the toner particles is used, silane alcohol may dissolve out of toner particle surfaces into the medium if the silane alcohol formed after hydrolysis has a high solubility, and the silane alcohol having dissolved out may mutually form particles independently. Hence, it is necessary to select a medium in which the silane alcohol obtained by hydrolyzing the silicon compound is slightly soluble.
When the polycondensation reaction of the silicon compound is allowed to proceed on the toner particles in which the silicon compound stands permeated, the speed of stirring depends on the concentration of particles in the system, the size of the system, the quantity in which the silicon compound stands permeated and so forth. Stirring at a too high speed or too low speed tends to cause the particles to coalesce one another and may cause a disorder of particle size distribution of the toner obtained. Accordingly, the speed of stirring must be controlled appropriately.
In the above case, commonly available surface-active agents, polymeric dispersants or solid dispersants may also be used in order to disperse the base-particle toner particles uniformly in the slightly water-soluble medium.
In the toner of the present invention, the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, formed on the toner particle surface, is a coating layer comprising a polycondensate of the silicon compound which is obtained by hydrolysis and polycondensation of the silicon compound such as a silane alkoxide in the manner as described above.
To obtain a filmlike polycondensate as described above, at least one type of silicon compound having at least two hydrolyzable and polycondensable groups in one molecule must be used. A monofunctional compound may be used in combination. Accordingly, in the present invention, the silicon compound usable to form the coating layer formed of silicon-compound-containing particulate matters being stuck to one another may include the following.
As a bifunctional or higher silane alkoxide, it may include, e.g., tetramethoxysilane, methyltriethoxysilane, hexyltriethoxysilane, triethoxychlorosilane, di-t-butoxyacetoxysilane, hydroxymethyltriethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetrakis(2-methacryloxyethoxy)silane, allyltriethoxysilane, allyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, bis(triethoxysilyl)ethylene, bis(triethoxysilyl)methane, bis(triethoxysilyl)-1,7-octadiene, 2,2-(chloromethyl)allyltrimethoxysilane, [(chloromethyl)phenylethyl]trimethoxysilane, 1,3-divinyltetraethoxydisloxane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane, methacrylamidopropyltriethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltrimethoxysilane, (3-methacryloxypropyl)trimethoxysilane, 1,7-octadienyltriethoxysilane, 7-octenyltrimethoxysilane, tetrakis(ethoxyethoxy)silane, tetrakis(2-methacryloxyethoxy)silane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane and vinyltriphenoxysilane.
The monofunctional compound which may be used in combination with the bifunctional or higher silane alkoxide may include, e.g.,
(3-acryloxypropyl)dimethylmethoxysilane,
o-acryloxy(polyethyleneoxy)trimethylsilane,
acryloxytrimethylsilane,
1,3-bis(methacryloxy)-2-trimethylsiloxypropane,
3-chloro-2-trimethylsiloxypropene,
(cyclohexenyloxy)trimethylsilane,
methacryloxyethoxytrimethylsilane and
(methacryloxymethyl)dimethylethoxysilane.
As a sol-gel reactive compound other than the silane alkoxide, an aminosilane as exemplified by 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane may also be used. Such a sol-gel reactive compound may be used alone or in combination of two or more.
In the sol-gel reaction, it is commonly known that the sol-gel films formed have a bond state which differs depending on the acidity of reaction medium. Stated specifically, when the medium is acidic, H+ adds electrophilicically to the oxygen of the alkoxyl group (xe2x80x94OR group) to become eliminated as an alcohol. Next, the water attacks nucleophilically and the corresponding moiety is substituted with the hydroxyl group. Here, the reaction of hydroxyl group substitution takes place slowly when the water in the medium is in a small content, and hence the polycondensation reaction takes place before all the alkoxy groups attached to the silane are hydrolyzed, to tend to relatively readily form a one-dimensional (simple) linear polymer or a two-dimensional polymer.
On the other hand, when the medium is alkaline, the alkoxyl group readily changes into a silane alcohol by nucleophilic substitution reaction attributable to OHxe2x88x92. Especially when a silicon compound having three or more alkoxyl groups in the same silane, the polycondensation takes place three-dimensionally to form a three-dimensional polymer rich in cross linkages, i.e., a sol-gel film having a high strength. Also, the reaction terminates in a short time. Accordingly, in order to form sol-gel films on the surfaces of toner particles serving as base particles, the sol-gel reaction may preferably be made to proceed under alkalinity. Stated specifically, the reaction may preferably be made to proceed under an alkalinity of pH 9 or higher. This enables formation of sol-gel films having a higher strength and a good durability.
The above sol-gel reaction may also fundamentally proceed at room temperature, but the reaction is accelerated by heating. Accordingly, a heat may optionally be applied to the reaction system.
A process in which the coating layer formed of silicon-compound-containing particulate matters being stuck to one another as described above is further treated with a coupling agent will be described below.
The coupling agent may commonly be expressed to be a molecule made up by combination of a reactive site and a functional site; the former being a metal alkoxide or metal chloride capable of combining with a functional group such as a hydroxyl group, carboxyl group or epoxy group lying bare to the material surface and the latter being an alkyl group or ionic group capable of imparting hydrophobicity or ionic properties to the material surface. In the present invention, the nature of this coupling agent that reacts with hydroxyl groups on the material surface is utilized, where, after the coating layer formed of silicon-compound-containing particulate matters being stuck to one another has been formed on the toner particle surface, the coupling agent is allowed to react with the silanol groups having remained thereon to cap the hydroxyl groups on the toner particle surfaces so that the toner can retain its charging performance in a good state even in an environment of high temperature and high humidity. Accordingly, an ideal coupling agent used in the present invention may preferably be a compound capable of readily reacting with silanol groups and in itself not allowing any unreacted metal alcohol groups to remain. Thus, compounds commonly called terminal stoppers or capping agents and compounds called silylating agents also have the function applicable to this purpose. Accordingly, in the present invention, these compounds are also defined to be coupling agents in a broad sense.
A process by which the coating layers formed on the toner particle surfaces are treated with the coupling agent will be described below.
As a method therefor, the coating layers may be treated by commonly available coupling treatment, capping treatment or silylating treatment. For example, it may include a method in which a coupling agent is added dropwise in an acidic alcohol solution whose pH has been adjusted to 4.5 to 5.5, and subsequently the toner particles surface-coated with a silane compound are introduced thereinto, where the reaction mixture is stirred for about 5 minutes, followed by repetition of filtration and washing, and then drying to separate treated toner particles; and a method in which a coupling agent is dissolved in alcohol and the coupling agent alcohol solution obtained is sprayed on a powder being agitated in a high-power mixer such as a twin coater, followed by agitation drying. To prepare the acidic alcohol solution in the former method, when an alkali is used in the reaction for forming on the toner particle surfaces the coating layers containing a silicon compound, the alkali may be removed or neutralized and thereafter an acid may be added in the same system to make adjustment to acidic, or the alkali is separated from the solution and the coupling treatment may be made in an acidic solution prepared anew.
In the toner production process of the present invention, it is also possible to mix the coupling agent at the time of the formation of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another, so as to make coupling treatment simultaneously with the formation of the coating layer. In this instance, silica monomers for forming the coating layer and the coupling agent may preferably be selected in such combination that the reactivity of the former is higher than the reactivity of the latter so that the mutual reaction of silica monomers proceeds first to form coating layers on the toner particle surfaces and thereafter the unreacted silanols on the coating layer surfaces react with the coupling agent to subject the coating layer surfaces to coupling treatment.
The coupling agent usable in the present invention may include, e.g., the following.
As a silica type coupling agent, it may include the following. First, as a bifunctional or higher silica type coupling agent, it may include, e.g., tetramethoxysilane, methyltriethoxysilane, hexyltriethoxysilane, triethoxychlorosilane, di-t-butoxydiacetoxysilane, hydroxymethyltriethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetrakis(2-methacryloxyethoxy)silane, allyltriethoxysilane, allyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, bis(triethoxysilyl)ethylene, bis(triethoxysilyl)methane, bis(triethoxysilyl)-1,7-octadiene, 2,2-(chloromethyl)allyltrimethoxysilane, [(chloromethyl)phenylethyl]trimethoxysilane, 1,3-divinyltetraethoxydisloxane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane, methacrylamidopropyltriethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltrimethoxysilane, 1,7-octadienyltriethoxysilane, 7-octenyltrimethoxysilane, tetrakis(ethoxyethoxy)silane, tetrakis(2-methacryloxyethoxy)silane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinyltriphenoxysilane and methacryloxypropyldimethoxysilane.
As a monofunctional silica type coupling agent, it may include, e.g.,
(3-acryloxypropyl)dimethylmethoxysilane,
o-acryloxy(polyethyleneoxy)trimethylsilane,
acryloxytrimethylsilane,
1,3-bis(methacryloxy)-2-trimethylsiloxypropane,
3-chloro-2-trimethylsiloxypropene,
(cyclohexenyloxy)trimethylsilane,
methacryloxyethoxytrimethylsilane and
(methacryloxymethyl)dimethylethoxysilane.
What is called a silylating agent may also be used as the coupling agent in the present invention, as exemplified by allyloxytrimethylsilane, trimethylchlorosilane, hexamethyldisilazane, dimethylaminotrimethylsilane, bis(trimethylsilyl)acetamide, trimethylsilyl diphenylurea, and trimethylsilyl imidazole.
As a titanium type coupling agent, it may include, e.g., o-allyloxy(polyethylene oxide)trisiopropoxytitanate, titanium allylacetoacetate triisopropoxide, titanium bis(triehtanolamine)diisopropoxide, titanium n-butoxide, titanium chloride triisopropoxide, titanium n-butoxide(bis-2,4-pentanedionate), titanium chloride diethoxide, titanium diisopropoxide(bis-2,4-pentanedionate), titanium diisopropoxide bis(tetramethylheptanedionate), titanium diisopropoxide bis(ethylacetoacetate), titanium ethoxide, titanium 2-ethylhexyoxide, titanium isobutoxide, titanium isopropoxide, titanium lactate, titanium methacrylate isopropoxide, titanium methacryloxyethylacetoacetate triisopropoxide, (2-methacryloxyethoxy)triisopropoxytitanate, titanium methoxide, titanium methoxypropoxide, titanium methyl phenoxide, titanium n-nolyl oxide, titanium oxide bis(pentanedionate), titanium n-propoxide, titanium stearyloxide, titanium tetrakis[bis-2,2-(allyloxymethyl)butoxide], titanium triisostearolyl isopropoxide, titanium methacrylate methoxyethoxide, tetrakis(trimethylsiloxy)titanium, titanium tris(dodecylbenzene sulfonate)isopropoxide, and titanocene diphenoxide.
As an aluminum type coupling agent, it may include, e.g., aluminum(III) n-butoxide, aluminum(III) s-butoxide, aluminum(III) s-butoxide bis(ethyl acetoacetate), aluminum(III) t-butoxide, aluminum(III) di-s-butoxide ethyl acetate, aluminum(III) diisopropoxide ethyl acetoacetate, aluminum(III) ethoxide, aluminum(III) ethoxyethoxyethoxide, aluminum hexafluoropentanedionate, aluminum(III) 3-hydroxy-2-methyl-4-pyrronate, aluminum(III) isopropoxide, aluminum 9-octadecenyl acetoacetate diisopropoxide, aluminum(III) 2,4-pentanedionate, aluminum phenoxide, and aluminum(III) 2,2,6,6-tetramethyl-3,5-heptanedionate.
Any of these may be used alone, may be used in plurality, or may be used in appropriate combination. The charge quantity of the toner may appropriately controlled by controlling the quantity of treatment to be employed.
There are no particular limitations on the quantity of treatment with the coupling agent. Treatment in a too large quantity may cause mutual combination of coupling agents to form coating films unwantedly to bring about a possibility of damaging fixing performance.
A process for producing the toner particles serving as base particles for the formation of the coating layer formed of silicon-compound-containing particulate matters being stuck to one another will be described below.
Polymerizable monomers usable when the base-particle toner particles are produced by polymerization may include, e.g., styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methoxystyrene, p-ethylstyrene and p-t-butylstyrene; acrylic acid monomers such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, n-propyl acrylate, isobutyl acrylate, octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, diaminomethyl methacrylate, dimethylaminoethyl methacrylate, benzyl methacrylate, crotonic acid, isocrotonic acid, acid phosphoxyethyl methacrylate, acid phosphoxypropyl methacrylate, acryloyl morpholine, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylonitrile, methacrylonitrile, and acrylamide; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, p-chloroethyl vinyl ether, phenyl vinyl ether, p-methylphenyl vinyl ether, p-chlorophenyl vinyl ether, p-bromophenyl vinyl ether, p-nitrophenyl vinyl ether, p-methoxyphenyl vinyl ether, and butadiene; dibasic acid monomers such as itaconic acid, maleic acid, fumaric acid, monobutyl itaconate, and monobutyl maleate; and heterocyclic monomers such as 2-vinylpyridine, 4-vinylpyridine, and N-vinyl imidazole. Any of these vinyl monomers may be used alone or in combination of two or more monomers, and may be used in any desired combination to select preferable polymer composition so that preferable properties can be attained.
As polymerization solvents (solvents in which polymerizable monomers are soluble but their polymers are insoluble) usable when the base-particle toner particles are produced by polymerization, those enabling products obtained by polymerization (i.e., polymers) to become precipitated with the progress of polymerization may be used. Stated specifically, they may include, e.g., straight-chain or branched aliphatic alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tertiary butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tertiary pentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethylbutanol, 1-heptanol, 2-heptanol, 3-heptanol, 2-octanol and 2-ethyl-1-hexanol; and aliphatic hydrocarbons such as butane, 2-methylbutane, n-hexane, cyclohexane, 2-methylpentane, 2, 2-dimethylbutane, 2,3-dimethylbutane, heptane, n-octane, isooctane, 2,2,3-trimethylpentane, decane, nonane, cyclopentane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, p-mentane and bicyclohexyl; as well as aromatic hydrocarbons, halogenated hydrocarbons, ethers, fatty acids, esters, sulfur-containing compounds, and mixture of any of these.
As polymeric dispersants usable in dispersion polymerization, they may specifically include, e.g., polystyrene, polyhydroxystyrene, polyhydroxystyrene-acrylate copolymers, hydroxystyrene-vinyl ether or vinyl ester copolymers, polymethyl methacrylate, phenol novolak resin, cresol novolak resin, styrene-acrylic copolymers, vinyl ether copolymers specifically as exemplified by polymethyl vinyl ether, polyethyl vinyl ether, polybutyl vinyl ether and polyisobutyl vinyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, a styrene-butadiene copolymer, an ethylene-vinyl acetate copolymer, vinyl chloride, polyvinyl acetal, cellulose, cellulose acetate, cellulose nitrate, alkylated celluloses, hydroxyalkylated celluloses specifically as exemplified by hydroxymethyl cellulose and hydroxypropyl cellulose, saturated alkyl polyester resins, aromatic polyester resins, polyamide resins, polyacetal, and polycarbonate resins; mixtures of these; and copolymers that can be formed by using in any desired proportion the monomers capable forming the polymeric compounds described above.
The toner of the present invention may be incorporated with a high-molecular-weight component or a gel component as a constituent of the toner so that melt-viscosity properties can be controlled as occasion calls, e.g., for anti-offset. The incorporation of such a component is achievable by the use of a cross-linking agent having at least two polymerizable double bonds per one molecule. Such a cross-linking agent may specifically include, e.g., aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; and compounds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol tetramethacrylate, glycerol acroxydimethacrylate, N,N-divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone.
Any of these may be used alone or in the form of an appropriate mixture of two or more compounds. The cross-linking agent may also previously be mixed in polymerizable monomers or may appropriately be added in the course of polymerization as occasion calls. The cross-linking agent used in the present invention may be in a concentration appropriately controlled taking account of molecular weight and molecular weight distribution of polymers produced. It may preferably be in a concentration within the range of from 0.01 to 5% by weight based on the total weight of polymerizable monomers used.
As the binder resin usable when the toner particles are produced by pulverization, it may include, e.g., polystyrene; homopolymers of styrene derivatives such as poly-p-chlorostyrene and polyvinyltoluene; styrene copolymers such as a styrene-p-chlorostyrene copolymer, a styrene-vinyltoluene copolymer, a styrene-vinylnaphthalene copolymer, a styrene-acrylate copolymer, a styrene-methacrylate copolymer, a styrene-methyl xcex1-chloromethacrylate copolymer, a styrene-acrylonitrile copolymer, a styrene-methyl vinyl ether copolymer, a styrene-ethyl vinyl ether copolymer, a styrene-methyl vinyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer and a styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenol resins, natural resin modified phenol resins, natural resin modified maleic acid resins, acrylic resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane resins, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resins, cumarone indene resins, and petroleum resins. Cross-linked styrene copolymers and cross-linked polyester resins are also preferred binder resins.
In the toner of the present invention, the binder resin may also be incorporated with a gel content in order to prevent offset from occurring at the time of melting.
As the colorant constituting the base-particle toner particles, any desired pigments or dyes may be used. Both of them may also be used in combination. For example, carbon black, magnetic materials, and colorants toned in black by the use of yellow, magenta and cyan colorants shown below may be used as black colorants.
As yellow colorants, compounds typified by condensation azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds and allylamide compounds are used. Stated specifically, C.I. Pigment Yellow 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 168, 174, 176, 180, 181 and 191 are preferably used.
As magenta colorants, condensation azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds and perylene compounds are used. Stated specifically, C.I. Pigment Red 2, 3, 5, 6, 7, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 144, 146, 166, 169, 177, 184, 185, 202, 206, 220, 221 and 254 are particularly preferred.
As cyan colorants, copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds and basic dye lake compounds may be used. Stated specifically, C.I. Pigment Blue 1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62 and 66 are particularly preferably usable.
Any of these colorants may be used alone, in the form of a mixture, or in the state of a solid solution.
In the case when a magnetic material is used as the colorant, it may preferably be added in an amount of from 40 to 150 parts by weight based on 100 parts by weight of the binder resin. In the case when other colorant is used, it may preferably be added in an amount of from 5 to 20 parts based on 100 parts by weight of the binder resin.
The toner of the present invention may also be incorporated with a magnetic material so that it can be used as a magnetic toner. In this case, the magnetic material may also serve as the colorant. The magnetic material usable in the present invention may include iron oxides such as magnetite, hematite and ferrite; metals such as iron, cobalt and nickel, or alloys of any of these metals with a metal such as aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten or vanadium, and mixtures of any of these.
The magnetic material used in the present invention may preferably be a surface-modified magnetic material. A surface modifier usable here may include, e.g., silane coupling agents and titanium coupling agents. These magnetic materials may also preferably be those having an average particle diameter of 1 xcexcm or smaller, and preferably from 0.1 xcexcm to 0.5 xcexcm. As the magnetic material, it is preferable to use those having a coercive force (Hc) of from 1.59xc3x97103 to 2.39xc3x97104 A/m (20 to 300 oersteds), a saturation magnetization ("sgr"s) of from 50 to 200 Axc2x7m2/kg (50 to 200 emu/g) and a residual magnetization ("sgr"r) of from 2 to 20 Axc2x7m2/kg (2 to 20 emu/g), as magnetic characteristics under application of 7.96xc3x97102 kA/m (10 K oersteds).
A charge control agent may optionally be added to the toner of the present invention. In such a case, any conventionally known charge control agents may be used. It is preferable to use charge control agents that make toner""s charging speed higher and are capable of stably maintaining a constant charge quantity. Stated specifically, they may include, as negative charge control agents, e.g., metal compounds of salicylic acid, alkylsalicylic acids, dialkylsalicylic acids, naphthoic acid or dicarboxylic acids, polymer type compounds having sulfonic acid or carboxylic acid in the side chain, boron compounds, urea compounds, silicon compounds and carixarene. As positive charge control agents, they may include, e.g., quaternary ammonium salts, polymer type compounds having such a quaternary ammonium salt in the side chain, guanidine compounds, and imidazole compounds. Any of these charge control agents may preferably be used in a amount of from 0.5 to 10 parts by weight based on 100 parts by weight of the binder resin.
In the toner of the present invention, for the purpose of improving the releasability required when used in combination with a heat roll fixing assembly, a low-temperature fluidity-providing component such as wax may be incorporated into the toner particles. The wax used here may include, e.g., paraffin wax, polyolefin wax and modified products of these (e.g., oxides or graft-treated products), higher fatty acids and metal salts thereof, higher fatty acid alcohols, higher fatty acid esters, and fatty acid amide waxes. Of these waxes it is preferable to use those having a softening point within the range of from 30 to 130xc2x0 C. as measured by the ring-and-ball method (JIS K2351). When such a wax is incorporated into the toner particles, it may preferably be added in the form of fine powder.
In the toner of the present invention, in order to control in an appropriate quantity the electric charge to be imparted to the toner particles, commonly available inorganic fine particles or organic fine particles such as silica, titania and alumina may auxiliarily used as an external additive.
There are no particular limitations on the particle diameter of the toner of the present invention, thus obtained. In order to have a high fluidity, the toner may preferably have a small particle diameter of from 0.1 to 10 xcexcm as its number-average particle diameter, and a sharp particle size distribution, having a coefficient of variation in number distribution of 20.0% or less. In order to achieve such particle diameter and particle size distribution, it may be necessary to employ what is called classification step in addition to the steps for toner production described previously. Accordingly, in the present invention, to avoid such a step, the dispersion polymerization mentioned previously may preferably be used when the base-particle toner particles are produced. The dispersion polymerization is commonly a process in which polymerizable monomers are polymerized in a polymerization solvent in which the monomers are soluble but the polymer obtained is insoluble, and in the presence of a particle stabilizer as typified by a polymeric dispersant. This is known as a process that can obtain particles with a uniform particle size distribution. Also, this dispersion polymerization is preferable for producing small-diameter toner particles having particle diameter of about 1 xcexcm to 5 xcexcm, as being preferable for the toner. Thus, in the present invention, the base-particle toner particles may preferably be produced by this dispersion polymerization.
The toner of the present invention, constituted as described above, may be used as a one-component type developer, or may be blended with a carrier so as to be used as a two-component type developer. When the two-component type developer is prepared by blending the toner of the present invention with a magnetic carrier, they may be blended in such a proportion that the toner in the developer has a concentration within the range of from 2 to 15% by weight. If the toner is in a concentration lower than 2% by weight, image density tends to lower. If on the other hand it is in a concentration higher than 15% by weight, fog and in-machine toner scatter tend to occur.
As the carrier, it is preferable to use a carrier having the following magnetic characteristics, i.e., to use a carrier having a magnetization intensity of from 30 to 300 kA/m (30 to 300 emu/cm3) at 79.57 kA/m (1,000 oersteds) after it has been saturated magnetically. If the carrier used has a magnetization intensity of 300 kA/m (300 emu/cm3) or above, toner images with a high image quality may be obtained with difficulty. If on the other hand it has a magnetization intensity of 30 kA/m (30 emu/cm3) or below, magnetic binding force may decrease to tend to cause carrier adhesion.
As described above, according to the present invention, the coating layer in a state of particulate matters being stuck to one another, containing at least a silicon compound (the coating layer formed of silicon-compound-containing particulate matters being stuck to one another) is provided on the toner particle surface. This can provide a toner which exhibits a good fluidity even without use of any fluidity-providing agent, can retain a stable electric charge quantity even in long-time running, and can form good images achievable of a high transfer efficiency.
In addition, according to the present invention, no fluidity-providing agent is used. Hence, a toner is provided which no longer has any possibility that the fluidity-providing agent becomes released from or buried in toner particles, even when development is repeated continuously, and can retain a good fluidity during running, promising a superior running performance.
According to the toner production process of the present invention, the toner having the above properties can be obtained with ease and stably.